Low power multi-band, multi-mode transmitter

ABSTRACT

A transmitter includes a power amplifier driver connected with a first transformer and a second transformer. The first transformer is configured for a first band mode and the second transformer is configured for a second band mode. The power amplifier driver drives both the first transformer and the second transformer.

1. PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.13/448,971, filed Apr. 17, 2012, which is incorporated herein byreference in its entirety.

2. TECHNICAL FIELD

This disclosure relates generally to communication systems and methods.More particularly, it relates to low-power, low-area and/or multi-band,multi-mode transmitters.

3. BACKGROUND

A transmitter or radio transmitter in electronics and telecommunicationsis an electronic device which with an antenna produces radio waves. Thetransmitter can generate a radio frequency alternating current, whichcan be applied to the antenna. When excited by the alternating currentthe antenna can radiate radio waves. The transmitter can be used inequipment that generates radio waves for communication purposes andradiolocation, such as radar and navigational transmitters. Generatorsof radio waves for heating or industrial purposes can also includetransmitters.

BRIEF DESCRIPTION OF THE DRAWINGS

The system may be better understood with reference to the followingdrawings and description. In the figures, like reference numeralsdesignate corresponding parts throughout the different views.

FIG. 1 is a block diagram of an exemplary communication environment.

FIG. 2 is a circuit diagram of an exemplary transmitter.

FIG. 3 is a circuit diagram of another example of the transmitter.

FIG. 4 is a circuit diagram of another example of the transmitter.

FIG. 5 is a circuit diagram of an exemplary mixer that can be used tomix signals for the transmitters described herein.

FIG. 6 is a circuit diagram of an exemplary transmitter in WCDMA/EDGEmode.

FIG. 7 is a circuit diagram of an exemplary transmitter in GMSK mode.

FIG. 8 is a circuit diagram of an exemplary gain control circuit.

FIG. 9 is a circuit diagram of another exemplary gain control circuit.

FIG. 10 is a circuit diagram of an exemplary local oscillator generator.

FIG. 11 is a circuit diagram for an exemplary low-pass filter design forthe transmitter.

DETAILED DESCRIPTION

The description below relates to a transmitter that can reduce powerconsumption and a die area versus some typical transmitters. A 2.7 Voltsupply to the power amplifier driver, which can be a main currentconsuming block of a cellular transmitter, can be replaced with a lowervoltage supply, such as about 1.5 Volts, or less. About twenty-fivepercent in power consumption may be saved without substantiallyimpacting a performance of the transmitter. Also, driver blocksincluding passive mixers can be shared among communication bands, whichcan improve the die area. Additionally, an active baseband low-passfilter can be replaced with a passive one, resulting in less powerconsumption, lower area and better noise performance. This transmitterarchitecture can be used for multi-band, multi-mode applications.

FIG. 1 is a block diagram of an exemplary communication environment 100.Communication signals can be sent between endpoints. In one example, theendpoint is a communication device 110, such as a cell phone, personaldigital assistant, tablet, portable email device, smartphone or aportable gaming system. The communication device can include atransmitter 112, a receiver 114, a memory 116, a processor 118 and anantenna 120 to wirelessly exchange information, e.g., emails, textmessages, radio, music, television, videos, video games, digitalinformation, etc., with other endpoints. The transmitter 112 andreceiver 114 can be configured separately or together, such as in atransceiver. The communication device 110 may also wirelessly connect toa radio receiver or other audio device such as earpiece 122.

The communication environment 100 can also include other endpoints suchas vehicles 130, such as automobiles, aircraft, ships and spacecraft.The communication environment 100 can also devices to provide acommunication link between the endpoints such as cellular towers 140 andsatellites 150. Transmitters 112 can also be component parts of manyelectronic devices that communicate by radio, such as wireless computernetworks, Bluetooth enabled devices, garage door openers, radar sets,and navigational beacons. The antenna 120 may be enclosed inside a caseor attached to the outside of the transmitter 112, as in portabledevices such as cell phones, walkie-talkies, and auto keyless remotes.

FIG. 2 is a circuit diagram of an exemplary transmitter 112. Thetransmitter 112 can provide both wide band code division multiple access(WCDMA) and enhanced data rate for global evolution/global system formobile (EDGE/GMS) communication channels, in the high band, e.g., 2 Ghz,and the low band, e.g., 1 Ghz. WCDMA and EDGE can receive IQ channelsand GSM can receive direct modulation from a phase-locked loop (PLL).Both the high and low bands can include dedicated radio frequency (RF)front-ends. Illustrated electronic components of the transmitter 112 maybe replaced by similar components having similar functions according toa specific application requirement or other considerations.

The transmitter 112 can be connected to local oscillators (LO) 200, 202that provide a frequency for signal modulation. The transmitter 112 caninclude a digital-to-analog converter (DAC) 204, such as one DAC for theI channel and one DAC for the Q channel. The DAC 204 converts digitalcodes to analog signals. The analog signals are then sent to a low passfilter (LPF) 206, for example a third order Chebyshev filter. There canbe one low pass filter for the I channel and one LPF for the Q channel.The LPF outputs a filtered analog signal to the frequency mixers 208 and210. The mixer 208 creates new frequencies from two signals: a 25%voltage-controlled oscillator frequency and the filter analog signalfrom the LPF 206. The mixer 210 creates new frequencies from twosignals: a 25% voltage-controlled oscillator frequency and the filteranalog signal from the LPF 206.

The mixers 208 and 210 can output up-converted, modulated analog signalsto power amplifier (PA) drivers 212 and 214, respectively. The PAdrivers 212, 214 output amplified signals to transformers 216, 218,e.g., balun transformer, respectively. Switches 220 and 222 connect theoutputs of the PA driver 212 and transformer 216 with ground to controlwhether the transmitter 112 is outputting in the high band WCDMA or thehigh band EDGE/GMS mode. Switches 224 and 226 connect the outputs of PAdriver 212 and transformer 218 to ground to control whether thetransmitter 112 is outputting in the low band WCDMA or the low bandEDGE/GMS mode. In this design the PA drivers 212 and 214 are linear andcan provide a power output about as high as 6 dBm. To accommodate WCDMAthere can be about an 800 millivolt swing up and down at the outputs ofthe PA driver 212 and 214 which can require about a 2.7 V supply.

FIG. 3 is a circuit diagram of another example of the transmitter 112.The transmitter 112 can operate at about 1.5 V, or less, and match abouta 50 ohm impedance with no external components. As discussed in moredetail in FIGS. 4 through 11 the gain control can be accomplished with asingle PA driver 300 for the low and high bands of the WCDMA andEDGE/GSM modes. The PA driver may provide for about 14-bit gain control.The PA driver 300 also connects with a single IQ mixer 302. The IQchannels can be converted for WCDMA and EDGE, and direct PLL modulationcan be used for GSM. The IQ mixer 302 receives filtered analog signalsfrom low pass filters 304 and 306, and LO from voltage-controlledoscillator 308 and outputs the modulated analog signal 310. The analogsignals can begin as digital signals from a digital signal processor312, including audio, video and/or data signals, and are converted toanalog signals with DACs 314 and 316. An exemplary DAC includes 10 bitresolution and 104M/112.8M clock frequency.

FIG. 4 is a circuit diagram of another example of the transmitter 112. Asingle PA driver 400 can drive two transformers 402 and 404 for the highand low bands. The transformer 402 can be optimized for high-bandtransmissions and the transformer 404 can be optimized for low-bandtransmissions. Switches 406, 408, 410 and 412 connect the transformers402 and 404 to ground to control whether the transmitter 112 istransmitting in high-band or low-band WCDMA or high-band or low-bandEDGE/GMS mode. Whichever switch 406, 408, 410 or 412 is open that is themode that is being transmitted. The outputs from the transformers 402and 404 can be single ended and the transmitter 112 can provide for 50ohm impedance.

Imbedded into the PA driver 400 is a multiplexer (MUX) 414. In otherimplementations the MUX can be separate from the PA driver 400. The MUX414 may be integrated into the PA driver 400 such as by incorporating asteering circuit, e.g., the steering circuit 640 described in FIGS. 6-9.Connected to the PA driver 400 is a single mixer 416 that handles boththe I and Q channels for high-band and low-band and WCDMA and EDGEmodes. An exemplary mixer is described in FIG. 5. The mixer 416 canallow for smaller loading of the local oscillator generation than ifmore than one mixer were used, such as in FIG. 2. The mixer 416 mixesthe local oscillator signal 418 with the filtered analog signal receivedfrom the DAC 420 and LPF 422. The local oscillator signal 418 can begenerated by local oscillator generator (LOGEN) 419, for example theLOGEN described in FIG. 10 or another LOGEN.

For Gaussian minimum shift keying (GMSK), e.g., GSM mode, the mixer 416can be off and a modulated voltage controlled output directly drives thePA driver 400 inputs. The DAC and the LPF can also be shut off since theGSM mode can be directly derived from the voltage controlled output,e.g., from the PLL. The mixed signal can be calibrated at the PA driver400 which can allow for single point calibration for both LOfeed-through and the image rejection ratio of the IQ channels, e.g.,across all bands and channels. The transmitter 112 can provide for lesspower consumption than if the number of mixers and PA drivers equaledthe number of transformers.

FIG. 5 is a circuit diagram of an exemplary mixer 500 that can be usedto mix signals for the transmitters 112 described herein. The mixer 500can be a passive mixer including switches 502, 504, 506 and 508 drivenby LOs. The LOs can be 25% clock signals delayed by quarter clockperiods. Other LO sizes and frequencies can also be used with thetransmitter 112. DACs 510 and 512 and LPFs 514 and 516 provide an analogfiltered signal to the switches 502, 504, 506 and 508. A PA driver 518connects with the outputs of the switches 502, 504, 506 and 508 toamplify the mixed analog signal.

FIG. 6 is a circuit diagram of an exemplary transmitter 112 in aWCDMA/EDGE mode. To filter and up-convert the analog signal, thetransmitter 112 can include LPFs 600 and 602 connected with mixer 604.The mixer 604 can include switches 606, 608, 610, 612, 614, 616, 618 and620. The switches can include low voltage, 40 nanometer n-channel MOSFET(NMOS) transistors. In other implementations PMOS or other types ofswitching devices can be used. Switches 606 and 608 can be driven by thelocal oscillator LO I+ channel, switches 610 and 612 can be driven bythe LO I− channel, switches 614 and 616 can be driven by the LO Q+channel, and switches 618 and 620 can be driven by the LO Q− channel.The mixer 604 sends an up-converted radio frequency (RF) signal at pointA and point B is the signal differential.

To provide gain to the RF signal, the RF signal is input to a gain unit622, such as a Gm unit, which includes metal oxide semiconductor (MOS)devices 624, 626, 628 and 630, or other switches. To control an amountof gain, if a voltage vdd is applied to switches 628 and 630 the gainunit 622 is on, otherwise the gain unit 622 is off. Therefore voltageVb1 is added to bias the cascode MOS devices 624, 626, 628 and 630. Thegain unit 622 can be implemented with an array of multiple gain unitsarranged on a chip, e.g. sixty-three gain units. The individual gainunits in such an array can contribute to the gain or not, depending onwhether they are turned on or not, allowing for six bits of gaincontrollability or about zero to 32 dB of gain control. For purposes ofsimplicity of explanation, only one gain unit 622 is illustrated.Capacitor/resistor elements 632 and 634 can be connected in parallel tothe inputs of the gain unit 622. The capacitor can be an alternatingcurrent (AC) couple capacitor passing the up-converted TX signals at theRF frequency from node A or B to the gates of the Gm units. The resistorcan provide the bias voltage Vb1 to the gates of the Gm unit. About a 4pico farad and about a 100 k ohm resister can be used.

After applying gain and to provide high-band and low-band multiplexerduties, an amplified signal 636 can outputted by the gain unit 622 tosteering circuit 640. The steering circuit 640 can include a high-bandsteering circuit M and a low-band steering circuit N. Other amounts ofsteering circuits can be used. The M circuit can include switches 642and 644 and the N circuit can include switches 646 and 648 forcontrolling band selection. If the M circuit is activated, for exampleby applying a high bias voltage Vb2, e.g., about 1.2 V, to switches 642and 644 and the N circuit is deactivated, for example by applying a lowvoltage Vb3, e.g. about 400 millivolt to switches 646 and 648, then thetransmitter 112 is operating in the high-band. If the N circuit isactivated, for example by applying a high voltage Vb3 to switches 646and 648 and the M circuit is deactivated, for example by applying a lowvoltage Vb2 to switches 642 and 644, then the transmitter 112 isoperating in the low-band.

The transmitter 112 can also include high-band transformer 660 andlow-band transformer 662 connected with the steering circuit 640. Inthis example, the transmitter is operating in the high-band so thehigh-band transformer 660 is shown connected to power amplifier (PA)670. In other examples the low-band transformer 662 is connected to acorresponding PA (not shown in FIG. 6). The transmitter 112 can alsoinclude capacitor arrays 680, 682, 684 and 686. The capacitor arrays680, 682, 684 and 686 can provide additional power to the amplifiedsignal 636 by ensuring that the signal is operating in the resonancefrequency for maximum gain. The capacitor array 680, 682, 684 and 686can be implemented with switched capacitors having variable capacitance.

In addition, the turn ratio of the primary windings of the transformer660 and 662 can be lowered from the typical turn ratio to lower theinternal voltage swings, e.g., to about less than 500 millivolts, whichallows for a lower supply voltage, such as 1.5 V instead of 2.7 V.Therefore, the voltage VDD applied to the transformers 660 and 662 topower the transmitter 112 can be reduced from 2.7 V to 1.5 V.

FIG. 7 is a circuit diagram of an exemplary transmitter 112 in GMSK(e.g. GSM) high-band mode. The LPFs and mixers (not shown here, seee.g., FIG. 6) are powered down for GMSK. In GMSK phase modulated mode aPLL divided output followed by buffer 700 directly drives the PA driver.The 25% duty-cycle oscillator block can be turned off and the original50% clock can drive the PA driver. The buffer 700 receives Ip, In andpower down (PD) inputs. The gain can be controlled by gain unit 622. Adummy buffer 710 can be included to provide load balancing between the Iclock and the Q clock. To operate in the low-band mode, N can beactivated and M deactivated by applying a high voltage to Vb3 and a lowvoltage to Vb2.

FIG. 8 is a circuit diagram of an exemplary gain control circuit 622,such as for a PA driver. In an embodiment there are 6 bits of gaincontrol in the gain unit 622, e.g., Gm unit, or sixty-three unity cellsX1 to X63. Different amounts of gain can be achieved by turning on oroff from zero to 63 units. Other amounts of units can be used. Forexample, for 7 bit gain control 127 units may be used.

FIG. 9 is a circuit diagram of another exemplary gain control circuit622, such as for a PA driver. Alternatively or in addition to the gainunit 622, the steering circuit 640 can be used to provide gain control.In this example, up to about 6 bits of gain control are provided by thesteering circuit 640. Other amounts of gain control can also be providedby increase or decreasing elements in the array of M and N devices.

For example, the M part 900 of the steering circuit 640 can include andetermined array of M devices. The M part may include sets of switches902, 904, 906 and 908. The switches can be constructed of differentwidths to provide for various voltage drops across them. For purposes ofexplanation, a first unit X1 of switches 902, 904, 906 and 908 mayinclude a device width of one micron. Moreover, a second unit X2 of foursimilar switches may include a two micron width, a third unit X4 may befour micron in width switches, a fourth unit X8 may be eight microns inwidth, a fifth unit X16 may be 16 microns and a sixth unit X32 mayinclude switches that are 32 microns in width. Other numbers of unitsand widths for the switches can be used. The same or similar setup canbe implemented for the N devices to provide additional gain in thelow-band.

For purposes of simplicity of explanation two units are described: afirst unit with switches of one micron in width and a second unit withswitches of two microns in width. Due to impedance caused by thedifferent widths, two-thirds of the current passes through the secondunit and one-third of the current passes through the first unit. Theunits in which a high voltage, e.g., about 1.2 V, is supplied to Vb4contribute to the gain and the units in which a low voltage, e.g., 400millivolts, is supplied to Vb4 do not contribute to the gain. Therefore,if high voltage is supplied to the first units and low voltage issupplied to the second units, one-third of the gain is added to theamplified signal 636. If low voltage is supplied to the first units andhigh voltage is supplied to the send units, two-thirds of the gain isadded to the amplified signal 636.

FIG. 10 is a circuit diagram of an exemplary local oscillator generator,e.g., that can be used to generate the LO signals for the transmitter112. A PLL loop can set frequency of the voltage-controlled oscillatoroutput 1000. A buffer 1002 receives the oscillator output 1000 to ensurebuffering of the PLL. In high-band mode, e.g., 2 Gb/s transmission rate,divider 1004 is on and dividers 1006 and 1008 are off. The dividers caninclude divide-by-two dividers or other divider values depending on animplementation. In low band-mode, e.g., 1 Gb/s transmission rate,dividers 1006 and 1008 are on and divider 1004 is off.

The circuit can also include a buffer 1010 connected with the output ofdivider 1004 and buffer 1012 connected with the output of dividers 1006and 1008. In the high-band mode buffer 1010 is on and buffer 1012 isoff, and in the low-band mode buffer 1010 is off and buffer 1012 is on.The dividers 1004, 1006 and 1008 and the buffers 1010 and 1012 can beturned on and off with power down signals PD_HB and PD_LB to controloperation in the high-band or low-band modes. The output 1040 of thebuffers 1010 and 1012 is a fifty percent clock IQ (50%) signal. Thebuffer output 1040 is sent to an AND gate and buffer 1014 to combine oneclock from the I channel and one clock from the Q channel to formtwenty-five percent clock IQ (25%) signals.

Instead of using a passive MUX, which can be lossy, to select betweenhigh-band and low-band modes, outputs of the buffers 1010 and 1012 canbe directly connected together due to an arrangement of the switchingcomponents of the buffers 1010 and 1012. When the buffers 1010 and 1012are off their buffer outputs 1040 act as open circuits. Gates of thePMOS devices of the buffers 1010 and 1012 can be connected to VDDthrough switch 1024 when the buffer is powered down (PD).

When the dividers 1004, 1006 or 1008 are off, the output 1030 is toground which grounds the buffers 1010 or 1012 too. When the dividers1004, 1006 or 1008 are on the buffers 1010 or 1012 can act as inverters.When the divider output 1030 is ground, the NMOS switch 1022 is off.Also, when divider output 1030 is ground, transmission switches 1026 and1028 are off. Therefore, the gate of PMOS switch 1020 is disconnectedfrom the divider output 1030. Also, switch 1024 connects VDD to the gateof PMOS switch 1020 to ensure that PMOS switch 1020 is disconnected fromthe output of the divider 1030. The switch 1024 can be sized to addsubstantially no capacitance to the circuit. In addition, switch 1020 isoff, e.g., its gate connected with VDD, switch 1022 is off and thebuffer output 1040 is an open circuit.

High-band and low-band buffers 1010 and 1012 can be implemented withswitching circuits, two of which are illustrated for the buffer 1012.For example, four circuits per buffer 1010 and 1012 can include one foreach of the clocks I+, I−, Q+ and Q−. The output of the I+ clock ofbuffer 1012 can be connected with, e.g., shorted to, the output of theI+ clock for buffer 1010. The output of the I− clock of buffer 1012 canbe shorted to the output of the I− clock for buffer 1010. The output ofthe Q+ clock of buffer 1012 can be shorted to the output of the Q+ clockfor buffer 1010. The output of the Q− clock of buffer 1012 can beshorted to the output of the Q− clock for buffer 1010. Since the buffer1010 or 1012 for the band that is off acts as an open circuit no outputinterferes with the buffer 1010 or 1012 that is on. The buffer output1040 can be sent to the AND gate/buffer 1014 to provide IQ (25%).

FIG. 11 is a circuit diagram for a low-pass filter design, such as forthe transmitter 112. The transmitter 112 can include a DAC 1100, asecond order passive LPF 1102, a buffer 1104, a mixer 1106 to mix LOwith an analog signal 1105 sent by the buffer 1104, a PA driver 1108, amultiplexer or steering circuit 1110, transformers 1112 and 1114, andswitches 1116, 1118, 1120 and 1122. The transmitter 112 can operate suchas described in any of FIGS. 4 through 10.

The second order passive LPF 1102 can be used by compensating in thedigital input of DAC 1100 for signal droop in the band. A digital inputof the DAC 1100 is configured to apply resistor/capacitor compensationinformation for the second order passive LPF 1102. There can be about0.6 dB droop for 2 Megahertz WCDMA or 100 Kilohertz EDGE.Resistor/capacitor (RC) calibration information can be used to determinein the amount of digital compensation required. For example, an inversetransfer function can be used with the RC calibration information todetermine the amount of digital domain compensation to apply to theinput of DAC 1100.

By changing from a third order active LPF to a second order passive LPFat least an op-Amp can be removed from the circuit. Therefore, an activebaseband low-pass filter can be replaced with a passive one and a buffer1104. The buffer 1104 can include low output impedance of about lessthan 5 ohms over the signal band. The buffer 1104 can include low outputnoise in the receiver (RX)-band, such as about 20 megahertz for 2G/8-PSKand 45 megahertz for 3G. The buffer 1104 can include high outputimpedance in the RX band to lower conversion gain for the noisecomponents. The buffer 1104 can achieve these features, for example, viafeedback.

The transmitter 112 may be used with various types of communicationsystems. The communication systems may include methods, devices, andlogic implemented in different combinations of hardware, software orboth hardware and software to utilize the transmitter 112. For example,communication functionality may be implemented using programmed hardwareor firmware elements (e.g., application specific integrated circuits(ASICs), electrically erasable programmable read-only memories(EEPROMs), controllers, microprocessors, combinations of elements,etc.), or other related components.

The functionality may be achieved using a computing apparatus that hasaccess to a code memory which stores computer-readable program code foroperation of the computing apparatus, in which case thecomputer-readable program code could be stored on a medium which isfixed, tangible and directly readable, (e.g., removable diskette,compact disc read only memory (CD-ROM), random access memory (RAM),dynamic random access memory (DRAM), read only memory (ROM), fixed disk,USB drive, or other machine-readable medium such as magnetic disk oroptical disk), or the computer-readable program code could be storedremotely but transmittable via a modem or other interface device (e.g.,a communications adapter) connected to a network (including, withoutlimitation, the Internet) over a transmission medium, which may beeither a non-wireless medium (e.g., optical or analog communicationslines) or a wireless medium (e.g., microwave, infrared or othertransmission schemes) or a combination thereof.

While various embodiments of the disclosure have been described, it willbe apparent that many more embodiments and implementations are possiblewithin the scope of the disclosure. Accordingly, the disclosure is notto be restricted except in light of the attached claims and theirequivalents.

What is claimed is:
 1. A transmitter, comprising: a power amplifierdriver; and a first transformer configured for a first band transmissionrate; and a second transformer configured for a second band transmissionrate, the first transformer and the second transformer connected withthe power amplifier driver, where the power amplifier driver drives boththe first transformer and the second transformer.
 2. The transmitter ofclaim 1, further comprising a mixer connected with the power amplifierdriver, the mixer configured to provide both first band and second bandmixed signals to the power amplifier driver.
 3. The transmitter of claim1, where the power amplifier driver is configured to provide both gaincontrol and first band and second band multiplexing.
 4. The transmitterof claim 1, where the power amplifier driver further comprises asteering circuit configured to select the first band transmission rateor the second band transmission rate.
 5. The transmitter of claim 4,where the steering circuit is configured to turn on at a first biasvoltage and turn off at a second bias voltage.
 6. The transmitter ofclaim 4, where the steering circuit is configured to apply gain to aradio frequency signal.
 7. The transmitter of claim 1, wherein the firsttransformer and the second transformer are powered by about a 1.5 voltsor less supply voltage.
 8. The transmitter of claim 1, furthercomprising a low pass filter connected with the power amplifier driver.9. The transmitter of claim 8, further comprising a digital-to-analogconverter connected with the low pass filter, where a digital input ofthe digital-to-analog converter is configured to applyresistor/capacitor compensation information for the low pass filter. 10.A transmitter, comprising: a low pass filter configured to filter ananalog communication signal; a mixer connected with the low pass filter,the mixer configured to mix the analog communication signal with a localoscillator signal to produce a mixed signal; and a power amplifierdriver connected with the mixer, the power amplifier driver including asteering circuit, the power amplifier driver configured to steer themixed signal to a first band transformer or a second band transformer.11. The transmitter of claim 10, where the steering circuit comprises afirst band steering circuit and a second band steering circuit.
 12. Thetransmitter of claim 10, where the steering circuit is configured toprovide gain to the mixed signal.
 13. The transmitter of claim 10, wherethe first transformer and the second transformer are powered by about1.5 volts or less.
 14. The transmitter of claim 10, where the low passfilter comprises a second order passive low pass filter.
 15. Thetransmitter of claim 14, further comprising a buffer connected with thesecond order passive low pass filter where the buffer provides about 5ohms or less output impedance to the analog communication signal. 16.The transmitter of claim 14, further comprising a digital-to-analogconverter connected with the second order passive low pass filter whereresistor/capacitor compensation information is applied to a digitalinput of the digital-to-analog converter.
 17. A local oscillatorgenerator for a transmitter, comprising: a first buffer to supply afirst transmission rate for a first band mode transformer; a secondbuffer to supply a second transmission rate for a second band modetransformer; and an output of the first buffer directly connected to anoutput of the second buffer, wherein the first buffer and the secondbuffer operate as an open circuit when off.
 18. The local oscillatorgenerator of claim 17, further comprising a gate connected with thefirst buffer and the second buffer to provide a twenty-five percentclock signal.
 19. The local oscillator generator of claim 17, where thesecond buffer include a circuit for the I+, I−, Q+ and Q− channels. 20.The local oscillator generator of claim 17, where the circuit comprisesa transmission switch to isolate an input to the second buffer from anoutput of the second buffer.